Garbd is packaged separately as part of Debian split packaging.
The garbd package in Debian is percona-xtradb-cluster-garbd-3.x.
The package contains garbd, daemon init script and related config files.
This package will be installed,
if you install the percona-xtradb-cluster-full-56 meta package.

Note

On Debian Jessie (8.0) and Ubuntu Xenial (16.04),
to stop or reload the node bootstrapped with servicemysqlbootstrap-pxc,
you’ll need to use servicemysqlstop-bootstrap
or servicemysqlreload-bootstrap respectively.
To check the status of the bootstrapped node,
run servicemysqlstatus-bootstrap.